Many squids, octopuses, and other mollusks (as well as some fish, amphibians, and reptiles) have chromatophores, specialized cells containing pigmentsthat can change the color of the skin. These cells respond to electrical impulses from the muscles, which means they can also respond to specific frequencies in the audible spectrum, namely 100 hz, or the bass frequencies of musical instruments.
Which means...a squid's chromatophores will react and change color with the beat of some deep, grimey beats! To see it in action, check out this amazing video:
Scientists (safely and humanely) connected an iPod to the dorsal side of a squid's fin. "When the iPod sends bass frequencies (<100Hz) the axons in the nerves have enough charge to fire an action potential. This will in turn cause the muscles in the chromatophores to contract."
So, the squid is literally going insane in its membrane. Nature is incredible.